1. Field of the Invention
This invention relates to a method and apparatus for dividing analog signals, and more particularly relates to a method and apparatus for the binary frequency division of analog signals in the microwave/millimeter bands.
2. Description of the Prior Art
As is known, frequency divider circuits are used to reduce the frequency of a signal by an integral multiple of the original frequency of the signal. For example, a typical frequency divider circuit would take a signal of frequency f and divide it down by the integer two to a frequency f/2.
There are various types of frequency dividers which are well known in the art. For example, there is the regenerative type of divider, illustrated schematically by FIG. 1. A regenerative divider basically includes a mixer 2, an amplifier 4 and a feedback loop 6. The output frequency, f.sub.out, goes around the loop and regenerates itself by combining with the input frequency, f.sub.in. If it is assumed that f.sub.out =f.sub.in /2, then the two frequencies combine in the mixer to form f.sub.in .+-.f.sub.out or f.sub.in /2 and 3 f.sub.in /2. Thus, the output signal contains f.sub.in /2 and its harmonics.
Although frequency division does occur in the regenerative divider described above, the divider has several shortcomings. The divider's output signal, Sf.sub.out, may contain two or more closely spaced frequencies near f.sub.in /2, rather than the desired signal at exactly f.sub.in /2. These closely spaced frequencies may regenerate each other so that they are prominent in the output signal. Accordingly, a regenerative type of divider tends to be narrowband in its application in that it must be tuned to the specific frequency it is being operated at.
Another disadvantage of the regenerative divider is that it requires a feedback loop. This complicates the operation of the divider.
For low frequencies, a digital divider may be used. However, because such dividers use "dynamic" or active components, they are generally limited to relatively low frequency operation only. An example of a digital divider, which has one of the highest operating frequencies (i.e. 14 GHZ), is Part No. UPG507 manufactured by NEC.
Examples of various frequency divider circuits are described in U.S. Pat. Nos. 3,305,730 (Parzen); 3,309,619 (Schucht); 3,605,023 (Kline, Jr.); and 4,641,101 (Selim).